The present invention relates to surface-modified particles, in particular inorganic-based particles, having reactive surfaces, in particular silane-reactive or siloxane-reactive surfaces, in particular hydroxyl-containing surfaces and/or particles consisting of or comprising metal or semi-metal oxides and/or hydroxides, preferably nanoparticles, which on their surface have a polysiloxane-based modifier, in particular having been reacted on their surface with a polysiloxane-based modifier, preferably with the formation of chemical, in particular covalent, bonds as well as a corresponding method for producing these surface-modified particles.
In addition the present invention relates to the use of these surface-modified particles, in particular in coating materials, and coating systems, in particular paints, colorants and the like, in dispersions of all types, in plastics, in foams, in cosmetics, in particular nail varnishes, in adhesives, in sealants, etc. Moreover, the present invention relates to the use of these surface-modified particles as fillers, in particular in the aforementioned systems.
In addition the present invention relates equally to systems, in particular coating materials and coating systems, in particular paints, colors and the like, plastics, foams and cosmetics, in particular nail varnishes, which contain these surface-modified particles. Finally, the subject matter of the present invention is also new dispersions which contain these surface-modified particles in a carrier or dispersant medium.
The use of particles, in particular nanoparticles, in coating and dispersion systems are fundamentally known to the skilled person from the prior art: thus, the use of nanoparticles as fillers for coating systems offers the advantage that a coating material obtains desired properties (e.g. increased scratch resistance) without adverse effects having to be taken into account at the same time (e.g. poor transparency).
It is known that the incorporation of nanoparticles into coating systems leads, for example, to the improvement in the mechanical properties of coating systems, for example in UV-curable coating systems.
Thus, for example, a method for the modification of nanoscale silica particles with alkoxysilanes which after incorporation into a corresponding UV-curable coating system provides an improvement in mechanical properties is described in EP 1 236 765 A1. Positive effects have also been found in other high-grade cross-linked systems such as, for example, in epoxide resins. The improvement in the mechanical properties is effectively explained by the binding of the nanoparticles to the surrounding matrix by means of chemical bonds. Owing to the chemical bonding of the particles to the organic matrix increasing embrittlement is observed, depending on the filler content of the coating material with such nanoparticles, and which depending on the field of application is detrimental for the coating. If the known silica-based nanoscale fillers are not bound to the organic matrix the desired effect of the improvement in the mechanical properties of UV-curable or epoxide-based coating systems is far less pronounced.
In addition to silica nanoparticles other types of nanoparticles may also be incorporated into coating materials in order to optimize their mechanical properties. For example, by addition of nanoscale aluminum oxide (e.g. the commercial products NANOBYK-3600 and NANOBYK-3601 of BYK-Chemie GmbH, Wesel, Germany) to UV-curable coating systems a clear improvement in abrasion resistance is achieved without effecting the flexibility of the system. In this case the aluminum oxide is not bound to the organic matrix of the coating system. The stabilization of the nanoparticles in the paint matrix is carried out with commercial wetting and dispersion additives.
Coating systems that are not UV-curable or are based on epoxide systems can likewise be optimized in respect of the scratch-resistance by the addition of nanoparticles.
Thus a method is described in U.S. Pat. No. 6,593,417 A in which silica particles in combination with a polysiloxane are used in a two-component polyurethane paint. The polysiloxane possesses reactive groups which can bind with the paint matrix through covalent groups. The bonding of the polysiloxane to the nanoparticles occurs merely by coordinative interactions. The specific combination of nanoparticles and polysiloxane effects orientation of the nanoparticles to the coating/air interface and leads to mechanical strengthening there, which is demonstrated by an increased scratch resistance. The orientation of the nanoparticles to the coating/air interface is disadvantageous since through stress on the coating through weathering and wear the uppermost layer is first removed and therefore the activity decreases with time.
U.S. Pat. No. 5,853,809 A teaches that an improvement in scratch resistance of coating systems that are used, for example, in automobile coating paints, can be achieved by the incorporation of modified nanoparticles. The modification of the nanoparticles is carried out, for example, with a functional polyurethane such that the polymer forms a covalent bond with the nanoparticle surface. Moreover, the polymeric shell of the nanoparticle modified in this way is able to participate in covalent bonds with the binding agent system of the coating material. Statements on the embrittlement of the paint system, especially at high nanoparticle contents, have not been made.
The modified nanoparticles from the prior art do indeed improve the scratch resistance of the paint in which they are used; but in particular with non-radiation-cured, in particular UV-crosslinked, systems the bonding of the nanoparticle by modification onto the paint matrix is particularly open to criticism: through the bonding of the nanoparticles to the paint matrix the network density of the cured paint film is increased, which leads to increased embrittlement of the paint film.
Nanoscale filler particles which are dispersed in a polymer matrix are known from DE 195 40 623 A1. Silanes, in particular organoalkoxysilanes, are described amongst others as surface modifiers. The surface modifiers are low-molecular weight compounds with a molecular weight that is not greater than 500 Dalton. The functional groups which such compounds must carry are determined by the surface groups of the nanoscale particles and the desired interaction with the matrix. The modified particles thus show an affinity for the matrix.
Thus the object on which the present invention is based is thus to provide surface-modified particles, in particular nanoscale surface-modified particles, which are in particular suitable for use in the afore mentioned systems and which at least essentially avoid or at least mitigate the disadvantages associated with the conventional particles as well as a corresponding method of production for such particles.
A further object of the present invention is seen in providing a new, efficient surface modification of particles of the type mentioned at the outset, in particular nanoparticles.
Furthermore, the object on which the present invention is based is to provide the particles, in particular nanoparticles, as stable dispersions in suitable dispersants and carriers (e.g. solvents, water, etc.) as they are used, for example in the surface coating industry. These new dispersions should have high storage stability even at high particle content. The tendency of these particle dispersions, in particular nanoparticle dispersions towards sedimentation or gel formation should be advantageously excluded. Moreover, the dispersions, in particular if they are used for the production of coating materials, should advantageously also bring about inter alia an increase in the scratch resistance of the cured coating. Any reactivity of the new surface-modified particles, in particular nanoparticles, towards the system in which they are used, in particular towards the binding agent component of the paint system, should be minimized as far as possible, preferably in order to avoid the tendency of the cured paint film towards embrittlement. In particular the surface modification must be as inert as possible or of as low reactivity as possible towards systems in which the surface-modified particles are used, in particular towards a paint matrix.
Finally a further object of the present invention is the provision of a production method for the new surface-modified particles, in particular nanoparticles, which can be carried out in a simple manner and can be varied widely, in particular in order to in this way tailor make new surface-modified particles, in particular nanoparticles, and their dispersions for different applications.
The applicant has now surprisingly found that the aforementioned object can be achieved in an efficient manner if particles, in particular inorganic-based particles with reactive groups, preferably silane- or siloxane-reactive groups, in particular hydroxyl groups on their surface and/or particles comprising or consisting of metal and/or semi-metal oxides, hydroxides and/or oxide hydroxide, preferably nanoparticles, are reacted with a polysiloxane-based modifier, preferably with the formation of chemical, preferably covalent, bonds, which have a higher molecular weight, preferably linear in structure, is inactive towards a surrounding matrix and is equipped with modifying, in particular polar groups. In this way the dispersibility of the particles is improved in a surprising manner, the surface modification improved over known systems, and the polarities better controlled.
To achieve the aforementioned object the present invention proposes surface modified particles according to the present disclosure. Further advantageous properties are described hereinafter.
Further subject matter of the present invention is a method for the production of the surface-modified particles of the invention according to the disclosure. Further advantageous properties are described.
Again, a further subject matter of the present invention is the use of the surface-modified particles of the invention as fillers according to the disclosure.
A further subject matter of the present invention is the use of the surface-modified particles of the invention as coating materials and coating systems, in particular paints, colorants and the like, in dispersions of all types, in plastics, in foams, in cosmetics, in particular nail varnish, in adhesives and in sealants according to the present disclosure.
Furthermore, subject matter of the present invention are likewise dispersions which contain the surface-modified particles of the invention in a carrier or dispersion medium according to the disclosure.
Finally a further subject matter of the present invention are coating materials and coating systems, in particular paints, colorants and the like, plastics, foams, cosmetics, in particular nail varnish, adhesives and sealants which contain the surface-modified particles of the invention according to the disclosure.
The present invention is described in detail on the basis of the surface-modified particles of the invention, in particular nanoparticles. The embodiments to this effect apply accordingly to the other aspects and subject matters of the present invention—production method of the invention, use of the invention, dispersions of the invention, etc—so that to avoid unnecessary repetition reference can be made hereunto also for the other aspects and subject matters of the present invention.